My iphone8 volume side buttons are. It working. I’m also not able to do a for e restart because of the volume buttons not working. I have looking in the settings and checked to make sure I am able to change volume by the buttons on the side of the phone but this is still not working. This has been an issue for about a month now and is very annoying.
Check: Settings>Sounds&Haptics>Change with buttons... should be ON (green).
If it is already ON, and your buttons don't produce any change, have your device inspected at your most convenient Apple Store or Authorized Service Provider (your iPhone should be still on warranty).
See this list: Apple - Find Locations - Location Selector
Regards
Giulio
Settings > Sounds & Haptics enable "Change with Buttons" then slide volume control all the way to the left. Once you do that you should be able to adjust volume with the two buttons on the upper left side of your iPhone8!
Iphone8 volume buttons
